Sputter ion pumps

ABSTRACT

To increase the ionization in sputter ion pumps, a relatively high vapor pressure metal is provided which vaporizes when heated by the discharge, the vaporized atoms are ionized and accelerated to the sputtering electrode to enhance the sputtering action which in turn increases the pump speed.

O 1 United States Patent 1191 1111 391,133

Hall Dec. 25, 1973 [54] SPUTTER ION PUMPS 3,542,488 11/1970 Hall 417 49 [75] Inventor: Lewis D. Hall, Palo Alto, Calif. OR PATENTS OR APPLICATIONS [73] Assignee: Veeco Instruments, Inc, Plainview, 909,640 7/1959 Great Britain 417/49 N.Y. Filed: Mar- 6 Primary Examiner-William Freeh Attorney-George B. Finnegan, Jr. et al. [21] Appl. No.: 231,828

1 I 57 ABST CT [52] US. Cl. 417/49 51 Int. Cl. F04b 37/02 To Tease the )mzatlm sputter Pumps a rela- [58] Field of Search 417/48 49 tively high vapor pressure metal is provided which vaporizes when heated by the discharge, the vaporized [56] References Cited atoms are ionized and accelerated to the sputtering electrode to enhance the sputtering action which in UNITED STATES PATENTS turn increases the pump speed. 2,336,138 12 1943 15 1 11 417 51 2,954,156 9/1960 Meyer 417/51 3 Claims, 1 Drawing Figure l lBi i l u /4 5 x HIGH M, VOLTAGE 6'0URCE l lB'i l i SPUTTER ION PUMPS BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to advances in ion pumping and particularly to improvements in electronic vacuum pumps of the cold cathode discharge type which operate on the principle of ion sputtering. In such pumps, gas molecules are ionized and the ions accelerated under the influence of an electric field to bombard a sputtering electrode of reactive material. The ionized molecules strike the electrode surface causing small amounts of reactive material to become dislodged or sputtered with the sputtered material forming a thin film on a gettering surface whereby the gas molecules are captured to provide the pumping mechanism. Detailed discussions of the phenomena will be found in the extensive literature on the subject.

Generally speaking, ion pumps have their performance dependent on the rate of ionization. At high vacua, the number of molecules available for ionization is relatively small, thus limiting pump performance.

It is a principal object of the present invention to overcome this shortcoming in the prior art without having to resort to complex and expensive heating, sublimation or other auxiliary mechanisms.

In accordance with the invention, a relatively high vapor pressure material is provided in the pump to provide a supply of vapor phase atoms for ionization. More particularly, the sputtering rate is increased by placing a metal having a relatively high vapor pressure in the region of the pump discharge. The high vapor pressure material'is heated by the discharge to provide metallic atoms in the vapor phase. These additional atoms are ionized and accelerated to the sputtering electrode(s) to provide additional sputtering and thereby increasing the pumping speed.

BRIEF DESCRIPTION OF DRAWING Having summarized the invention, there follows a detailed description with reference for illustrative purposes to the accompanying drawing forming part of the specification, which is a partially diagrammatical crosssectional view of an improved ion pump in accordance with the invention.

DETAILED DESCRIPTION An ion pump embodying the present invention is illustrated in the figure. The pump is provided with an envelope 10 formed with an inlet 11 to a pump chamber 13 wherein the pumping elements are housed. The pumping elements conventionally include a cellular anode 15 formed of a plurality of axially aligned anode cells 14, and a sputtering electrode 16 disposed to one side of the anode l5. Electrode 16, which is constructed of a reactive gettering material such as titanium, is illustratively in the form of a flat plate extending substantially parallel to the major plane of the anode 15 providing a perpendicular surface to the axial discharges of the individual anode cells 14.

A high voltage source 18 is connected to the anode 15 through an insulator 21 while the sputtering electrode 16 is connected to a lower potential, illustratively shown as ground, through an insulator 22. Two magnetic core pieces 19 and 20 oppositely disposed outside of envelope l establish magnetic field B within the chamber 13 extending axially of the anode cells 14 in the direction shown and in conventional manner.

Assuming the pressure in chamber 13 has been roughed to 10' Torr or below, the conventional aspect of operation of the ion pump is as follows. Upon establishing a sufficiently high potential on the anode 15 relative to the sputtering cathode 16, a discharge is pro duced which results in electrons flowing from the cathode to the anode. However, the magnetic field prevents the electrons from hitting the anode, but causes them to oscillate back and forth; en route, they thus collide with molecules of the gas being evacuated that are present in the space betwen the two electrodes, thereby converting the molecules into positive ions which are attracted to the negatively charged sputtering electrode 16. The ionized particles strike the sputtering electrode causing reactive material to sputter from the cathode surface and deposit as a thin film, principally on the anode surface. The gettering action of this thin reactive film provides the principal mechanism by which gas molecules are pumped. As will be appreciated, it is extremely important in the pump operation that this thin reactive film be continuously renewed by sputtering.

It can be seen that at low pressures there are relatively few molecules available for ionization and sputtering.

In accordance with the invention, the ion pump is provided with a separate high yield source of metallic atoms in the gas phase for ionization and sputtering comprising a metal having a relatively high vapor pressure, e.g., magnesium or manganese. The high vapor pressure metal is heated to yield atoms in the vapor phase which are ionized in the discharge for sputtering. Localized heating is conveniently accomplished by the pump discharge.

Referring again to the figure, the high vapor pressure metallic source is embodied as a second electrode 17 connected to ground through the insulator 22, as shown. The high vapor pressure electrode 17 is illustratively in the form of a flat plate disposed in parallel relation to the sputtering electrode 16 on the opposite side of the anode 15.

It has been found that the separate atomic source provided by the high vapor pressure metal electrode gives improved performance over the entire pump operating range. Contrary to what might be expected, the presence of the high vapor pressure material in the vacuum chamber does not have a limiting effect on the ultimate pressures attainable.

What is claimed is:

l. The method of enhancing the low pressure pump ing mechanism of sputter ion pumps having a discharge and at least one reactive sputtering cathode comprising the steps of:

A. heating a high yield atomic source of high vapor pressure material to produce atoms in the vapor phase;

B. subjecting the vapor atoms to the pump discharge to cause ionization thereof;

C. allowing said ions to bombard the reactive sputtering cathode thereby increasing the sputtering action of said cathode.

2. The method of enhancing the low pressure pumping mechanism of sputter ion pumps having a discharge and at least one reactive sputtering cathode as described in claim 1 wherein the step of heating a high yield atomic source of high vapor pressure material to produce atoms in the vapor phase is accomplished by heating magnesium.

3. The method of enhancing the low pressure pumping mechanism of sputter ion pumps having a discharge and at least one reactive sputtering cathode as de- 

1. The method of enhancing the low pressure pumping mechanism of sputter ion pumps having a discharge and at least one reactive sputtering cathode comprising the steps of: A. heating a high yield atomic source of high vapor pressure material to produce atoms in the vapor phase; B. subjecting the vapor atoms to the pump discharge to cause ionization thereof; C. allowing said ions to bombard the reactive sputtering cathode thereby increasing the sputtering action of said cathode.
 2. The method of enhancing the low pressure pumping mechanism of sputter ion pumps having a discharge and at least one reactive sputtering cathode as described in claim 1 wherein the step of heating a high yield atomic source of high vapor pressure material to produce atoms in the vapor phase is accomplished by heating magnesium.
 3. The method of enhancing the low pressure pumping mechanism of sputter ion pumps having a discharge and at least one reactive sputtering cathode as described in claim 1 wherein the high vapor pressure material is heated by subjecting said material to the pump discharge. 